The present application relates generally to optical diagnosis using aberration measurements, and relates more particularly to the use of one or more sequences of aberration measurements to produce an optical diagnosis. In many embodiments, a sequence of aberrations measurements are obtained and used to quantify the aberrations of an eye. The quantified aberrations are then used to produce an optical diagnosis for the eye.
Known laser eye procedures generally employ an ultraviolet or infrared laser to remove a microscopic layer of stromal tissue from the cornea of the eye to alter the refractive characteristics of the eye. The laser removes a selected shape of the corneal tissue, often to correct refractive errors of the eye. Ultraviolet laser ablation results in photo-decomposition of the corneal tissue, but generally does not cause significant thermal damage to adjacent and underlying tissues of the eye. The irradiated molecules are broken into smaller volatile fragments photochemically, directly breaking the intermolecular bonds.
Laser ablation procedures can remove the targeted stroma of the cornea to change the cornea's contour for varying purposes, such as for correcting myopia, hyperopia, astigmatism, and the like. Control over the distribution of ablation energy across the cornea may be provided by a variety of systems and methods, including the use of ablatable masks, fixed and moveable apertures, controlled scanning systems, eye movement tracking mechanisms, and the like. In known systems, the laser beam often comprises a series of discrete pulses of laser light energy, with the total shape and amount of tissue removed being determined by the shape, size, location, and/or number of a pattern of laser energy pulses impinging on the cornea. A variety of algorithms may be used to calculate the pattern of laser pulses used to reshape the cornea so as to correct a refractive error of the eye. Known systems make use of a variety of forms of lasers and/or laser energy to effect the correction, including infrared lasers, ultraviolet lasers, femtosecond lasers, frequency multiplied solid-state lasers, and the like. Alternative vision correction techniques make use of radial incisions in the cornea, intraocular lenses, removable corneal support structures, thermal shaping, and the like.
Known corneal correction treatment methods have generally been successful in correcting standard vision errors, such as myopia, hyperopia, astigmatism, and the like. However, as with all successes, still further improvements would be desirable. Toward that end, wavefront measurement instruments are now available to measure the refractive characteristics of a particular patient's eye.
One promising wavefront measurement system is the iDESIGN ADVANCED WAVESCAN STUDIO System, which includes a Hartmann-Shack wavefront sensor assembly that may quantify higher-order aberrations throughout the entire optical system, including first and second-order sphero-cylindrical errors and third through sixth-order aberrations caused by coma and spherical aberrations. With advanced algorithms for measuring and applying the wavefront correction (e.g. Fourier or zonal), even higher spatial frequency structures can be corrected, providing that adequate registration can be maintained between the intended correction and its application in a practical system. The wavefront measurement of the eye creates a high order aberration map that permits assessment of aberrations throughout the optical pathway of the eye, e.g., both internal aberrations and aberrations on the corneal surface. Thereafter, the wavefront aberration information may be saved and thereafter input into a computer system to compute a custom ablation pattern to correct the aberrations in the patient's eye. A variety of alternative wavefront or other aberration measurement systems may also be available
Customized refractive corrections of the eye may take a variety of different forms. For example, lenses may be implanted into the eye, with the lenses being customized to correct refractive errors of a particular patient. By customizing an ablation pattern or other refractive prescription based on wavefront measurements, it may be possible to correct minor refractive errors so as to reliably provide visual acuities better than 20/20. Alternatively, it may be desirable to correct aberrations of the eye that reduce visual acuity, even where the corrected acuity remains less than 20/20.
The determination of a customized refractive correction for an eye may be complicated by the often dynamic nature of the refraction of an eye. The optical aberrations of an eye can vary with, for example, changes in viewing conditions such as viewing distance and/or illumination. Changes in aberrations due to changes in viewing distance can become especially significant as a person ages and presbyopia sets in. Even for viewing distances within an accommodation range of an eye, different accommodation levels have different levels of muscular contraction, which may result in different aberrations due to, for example, changes in the shape of the eye arising from different internal strain levels in the eye. Even changes in the moisture level of the eye (e.g., tear film) can produce changes in the aberrations of the eye.
Consequently, multiple aberration measurements may be required to accurately characterize the aberrations of an eye. Thus, improved methods and systems that use one or more sequences of aberration measurements to accurately characterize the aberrations of an eye are desirable. Likewise, improved methods and systems for determining a customized refractive correction for an eye are also desirable.